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seven-up controls switching of
transcription factors that specify temporal
identities of Drosophila neuroblasts
Kanai MI, Okabe M, Hiromi Y.
Developmental Cell, 8(2) 203-213, 2005
Drosophila neuronal stem cell neuroblasts (NB)
constantly change character upon division, to
produce a different type of progeny at the next
division. Transcription factors Hunchback (HB),
Kruppel (KR), Pdm (PDM), etc. are expressed
sequentially in each NB and act as determinants of
birth-order identity. How a NB switches its
expression profile from one transcription factor to
the next is poorly understood. We show that the
HB-to-KR switch is directed by the nuclear receptor
Seven-up (SVP). SVP expression is confined to a
temporally restricted subsection within the NB's
lineage. Loss of SVP function causes an increase in
the number of HB-positive cells within several NB
lineages, whereas misexpression of svp leads to the
loss of these early-born neurons. Lineage analysis
provides evidence that svp is required to switch
off HB at the proper time. Thus, svp modifies the
self-renewal stem cell program to allow
chronological change of cell fates, thereby
generating neuronal diversity.
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Typical stem cell (left)
produces only one kind of progeny through
"self renewal" type of cell division.
Neural stem cells (middle) generates a
large variety of neuronal and glial cell
types, by changing its expression pattern
of transcription factors such as Hunchback
(HB) and Kruppel (KR). Kanai et al. show
that this HB-to-KR switch is controlled by
Nuclear receptor Seven-up. In
seven-up mutant (right),
neuroblasts continue to produces the same
kind of neurons, as if "reverting" to the
self renewal type division.
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